The present invention relates to rock drilling equipment, and more particularly to drill bits used with down-hole drills.
Referring to FIGS. 1 and 2, percussive down-hole drills 1 are well known and each typically includes a drill casing 2 and a piston (not shown) slidably retained within the casing 2. A chuck 3 is mounted to a lower end 2c of the casing 2 and a drill bit 4 is mounted within the casing 2 so as to be slidable through the chuck 3. The drill bit 4 has a lower, working end 4a that extends outwardly from the casing 2 so as to be contactable with material of a work site (e.g., where a hole is being drilled). The piston (not shown) impacts the bit 4 such that the bit 4 transfers the impact force to the material (e.g., rocks, earth, etc.) to cause the material to fracture apart into removable pieces.
One type of percussive drilling device called a xe2x80x9ccluster drillxe2x80x9d 5 is formed of a plurality of separate down-hole drills 1 mounted within a large cylindrical case 6. As a cluster drill typically includes several individual drills 1, and thus several drill bits 4, a substantial amount of time is required to change all of the bits 4, which becomes necessary when the bit working ends 4a become worn down through use. The required maintenance is increased by the relatively difficult process of removing and installing each bit 4 mounted within the casing by known retainer devices 7, which are typically two half-ring segments 7a, 7b, as discussed below. For one type of known cluster drill 5 having fifteen (15) separate drills 1, the average time to change the bit 4 of each drill 1 is approximately 30-45 minutes, such that the time to remove and replace all of the bits 4 is estimated at one complete ten-hour day using a three person crew.
Referring particularly to FIG. 2, a typical process for removing a bit 4 from a down-hole drill 1 proceeds as follows. First, a backhead nut 8 is un-threaded from the upper, backhead portion (not shown) of the individual drill 1 (FIG. 2a), which thereby releases the individual drill 1 from the cluster case 6 (FIG. 2B). Next, the released drill 1 is placed in a threaded xe2x80x9cjoint breakingxe2x80x9d device (not shown) which is used to unthread the threaded joint between the casing 2 of the particular drill 1 and the chuck 3 mounted to the lower end 2b of the casing 2 (FIG. 2C). Due to the high torque required both to loosen the backhead nut 8 and to xe2x80x9cbreakxe2x80x9d the threaded chuck-casing joint, relatively heavy and cumbersome equipment (not shown) is required to perform these functions.
As shown in FIG. 2D, the chuck 3 is then un-threaded from the drill casing 2, releasing the chuck 3, the drill bit 4 and the retaining ring segments 7a, 7b from the casing 2. The ring segments 7a, 7b are then removed from the chuck-and-bit assembly (FIG. 2E) and the chuck 3 is slided off of the drill bit 4 (FIG. 2F). After the bit 4 is replaced by a new bit 4, the above-described steps are executed in reverse to install the bit 4 within the chuck 3, the chuck 3 and bit 4 assembly within the individual drill casing 2 and finally the drill 1 into the cluster casing 6.
Thus, it would be desirable to have a bit retaining device that reduces the amount of time and effort to install and remove the bits 4 of down-hole drills 1.
In one aspect, the present invention is a device for retaining a drill bit connected with a casing of a percussive drill assembly. The casing has a central axis and the bit has a generally cylindrical head. The retainer device basically comprises a generally annular body having a central axis and an inner circumferential shoulder portion projecting generally toward the axis. The body is disposeable within the casing such that the body axis is substantially collinear with the casing axis. The shoulder is deflectable between a first position, where the shoulder is contactable with the bit head to retain the bit disposed at least partially within the retainer body, and a second position. The second position is spaced radially outwardly from the first position such that the bit head is displaceable through the body in a direction generally along the casing axis.
In another aspect, the present invention is a drill assembly comprising a casing having a hollow interior and a central axis and a drill bit having a generally cylindrical head. A generally annular retainer is disposed within the casing interior and has an inner circumferential shoulder projecting generally toward the casing axis. The shoulder is deflectable between a first position, where the shoulder is contactable with the bit head to retain the bit disposed at least partially within the retainer, and a second position. The second position is spaced radially outwardly from the first position such that the bit head is displaceable through the retainer in a direction generally along the casing axis.